Problem

We've got highload app and use inmemory cache, we want to optimize it everywhere we could.

Question

How much weight of each variable type? I mean:

• Boolean as value
• Emty string is value
• null I want to use something like that

cache.set(key, '') // emty string as value
// or
cache.set(key, true) // we don't need any value, we just need check keys 

CodePudding user response：

(V8 developer here.)

It doesn't matter which of these options you pick. null, true, false, and "" all exist anyway. Storing a reference to either of them always takes the same amount of memory (namely 4 bytes; or 8 on Node without pointer compression).

In fact, this principle goes even further. I assume you'll have many of these cache entries. So you could even define an object of your own (if that'd be useful in any way), and as long as you only have one of these objects and many references to it, the size of the object practically doesn't matter.

Example:

let big = new Array(1000);  // About 4000 bytes.
let small = {answer: 42};   // About 16 bytes. (Simplifying a bit.)

for (let i = 0; i < 1000; i  ) cache1.set(i, big);
for (let i = 0; i < 1000; i  ) cache2.set(i, small);
for (let i = 0; i < 1000; i  ) cache3.set(i, "");
for (let i = 0; i < 1000; i  ) cache4.set(i, null);
for (let i = 0; i < 1000; i  ) cache5.set(i, true);

After doing this, all caches cache1 through cache5 will all have the exact same size: they're each storing 1000 references. It doesn't matter what these references are referring to. (I can't say how many bytes it'll be because I don't know what you're using as cache implementation. If it's a Map, then memory consumption is about 12-20 bytes per entry on average, fluctuating because the backing store is grown in rather large infrequent steps.)